1. Field of the Invention
This invention relates to the installation of cable and, more particularly, to a cable block for temporarily supporting a section of aerial cable prior to its being lashed to a supporting strand.
2. Description of the Prior Art
In the installation of aerial cable, a so-called lashing method is employed wherein the cable is secured to a supporting strand (or so-called messenger) by wrapping a fairly large gage lashing wire in spiral fashion therearound. Prior to the lashing operation, the aerial cable is temporarily supported in close proximity to the strand by a plurality of cable blocks mounted on the strand, and typically spaced apart at intervals ranging from 10 to 20 feet along a given span thereof, i.e., between a pair of utility poles. The cable blocks are subsequently cumulatively pushed along each successive span of the strand by and ahead of a lashing machine. Upon reaching any given pole defining the end of a lashed cable span, the then stacked array of cable blocks are removed from the strand by a workman, and re-mounted in a spaced array along the next succeeding span of the strand. Thereafter, the lashing machine is also transferred to the other side of the then adjacent pole, and positioned on the strand in front of the first re-mounted cable block in readiness for lashing a new section of cable to the strand along that particular span. In some applications, new cable is lashed to existing cable previously lashed to the strand.
In such an aerial cable installation, it is appreciated that the cable blocks should be constructed such that they are reliably and easily mounted on the supporting strand, and readily movable in singular and tandem fashion therealong in the direction of movement of the lashing machine. It is also very important, however, that such a cable block incorporate means to effectively lock it with respect to longitudinal movement in the opposite direction.
Effective unidirectional locking of the cable blocks is very important as the un-lashed cable supported thereby tends to exert variable and appreciable longitudinally directed forces on the blocks in the direction of the lashing machine. Such forces are most pronounced during the threading of a winch line over the respective pulleys of the spaced array of cable blocks, and while the free end of a new reel of cable is pulled thereby over the rollers preparatory to the lashing of that unwound reel of cable to the supporting strand. Even after a portion of a new unwound reel of cable has been temporarily supported by the spaced array of cable blocks along any given span between two utility poles, any excess length of such cable that extends between the last cable block and the ground (or supply reel on the ground) will exert a substantial longitudinal force, in the direction of the lashing machine, against that block initially and, thereafter, possibly against one or more adjacent blocks in a cumulative fashion if they are allowed to become bunched. Thus, unless a positive locking mechanism is incorporated in the cable blocks to prevent such displacement, they can very readily defeat the purpose intended therewith.
It is also important that the cable blocks grip the strand such that they remain in a substantially vertically oriented position at all times so as to facilitate the guiding of the cable therethrough, as well as through the lashing machine. This also minimizes any tendency of the cable blocks to become jammed on the strand while being cumulatively pushed in tandem by the lashing machine, and also minimizes the possibility that the blocks could become accidentally dislodged from the strand due to very strong gusts of wind, for example.
A prior cable block intended to provide all of the above-noted operating characteristics is disclosed in O. L. Walter patent, U.S. Pat. No. 3,134,575. That cable block utilizes a single spring-biased and pivotally mounted cam to effect the locking of the cable block from movement along the strand in one particular direction, while allowing relatively free movement in the opposite direction. The single cam employed is dimensioned and positioned such that it engages the strand from only one laterally disposed side thereof, and in a region where the frame on the cable block does not provide any form of a mutually disposed backstop so as to provide a symmetrical gripping or wedging action against the strand, i.e., from opposite sides thereof.
As a result, the single locking cam mechanism in question has been found to not always maintain the cable block vertically oriented on the strand while supporting a section of cable and being pushed along the strand, particularly during high wind conditions, because of the asymmetrical cam force exerted against the strand. In addition, such a mechanism has also been found to not always provide the degree of positive locking action desired, particularly during the aforementioned winch-line pull-through of a new length of cable, or when hilly terrain is involved.
In addition to the aforementioned desired and important operating characteristics that have been urgently sought in cable blocks heretofore, there has also been a need for a cable block that could be readily adjusted or controlled so as to selectively allow movement in either direction and, conversely, to selectively allow oppositely directed locking action, for a given as-mounted orientation of the block on the strand. This would be of particular advantage, for example, in allowing the open side of the asymmetrical cable blocks to be positioned on a given side of the support strand either because of adverse wind conditions, uneven terrain, or because of the close proximity of obstructions, such as trees or buildings along a particular span or spans of the supporting strand.